Proteoglycans (PGs) are conjugates of glycosaminoglycans and protein. No precise biological role has been assigned to these substances, but they are thought to be involved in cellular adhesion and in the maintenance of the integrity of the extracellular matrices. We have continued our studies on cell surface PGs by isolating PGs and by studying their distribution and interactions with other macromolecules. During the past year we have shown: (1)\that the core proteins of heparan sulfate PG and a chondroitin sulfate PG are immunologically different and that both differ from the high molecular weight cartilage proteoglycan; (2)\that chondroitin sulfate PG interacts with collagen and fibronectin and reduces the adhesiveness of cells to matrices constructed from these proteins; and (3)\that transformed cells lack cell surface heparan sulfate PG, which in the normal cells codistributes with fibronectin and laminin, but retain chondroitin sulfate PG. These studies suggest that structurally different PGs serve different functions at the cell surface and that some of them may be important modifiers of cell adhesion. We are currently preparing monoclonal antibodies to chondroitin sulfate PGs isolated from human fetal membrane tissue. These antibodies will provide improved reagents for the study of the molecular heterogeneity of PGs and will allow studies on their tissue distribution and expression in normal and malignant cells.